• 대한기계학회논문집B
• /
• 제35권12호
• /
• pp.1257-1264
• /
• 2011

희박예혼합 가스터빈 연소기에 대한 3 차원 RANS 해석을 수행하였으며 PCFM(Partially Premixed Coherent Flame Model) 화염면적밀도 생성항 상수의 보정을 통하여 희박연소조건을 모사하였다. PCFM 에서 계산된 화염면적밀도에 의해 층류 예혼합 화염의 전파를 예측하고 불균일하게 분포한 기연 가스의 물성을 평형 가정에 따라 예측하였다. 복사와 대류 열전달을 모사하기 위해 냉각 조건으로서 실험과의 비교를 통해 결정된 열유속을 적용하였다. 이러한 3 차원 해석 결과를 바탕으로 파일럿 노즐과 메인 노즐에 분배되는 연료량 비에 대한 민감도 조사를 수행하였으며 CRN(Chemical Reactor Network)을 구성하여 NOx 배출량을 예측하고 측정값과 비교 분석하였다.

• 한국음향학회지
• /
• 제37권2호
• /
• pp.92-98
• /
• 2018

본 논문은 모형 프로펠러를 대상으로 공동수조 시험, 수중 충격시험, 유한요소해석 및 전산유체해석에 기반하여 수행한 명음 발생 메커니즘 연구이다. 선미 유동을 모사하기 위해 반류망, 프로펠러 및 방향타를 설치하고 수중청음기와 가속도계로 프로펠러 명음 현상의 발생과 소멸을 계측하였다. 유한요소해석을 통해 프로펠러 날개의 고유진동수를 예측하고 접촉 및 비접촉식 충격시험으로 이를 검증하였다. RANS(Reynolds Averaged Navier-Stokes) 방정식 기반 전산유체해석을 통하여 프로펠러 날개 각 단면의 유속과 유효 받음각을 계산하였으며, DES(Detached Eddy Simulation) 기반 고해상도 해석을 통해 명음 발생 위치에서 2-D 날개 단면 뒷전의 와류흘림주파수(vortex shedding frequency) 계산을 수행하였다. 수치적으로 예측된 와류흘림주파수는 모형시험으로 계측한 명음 발생 주파수 및 날개 고유진동수와 일치함을 확인하였다.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2007년도 춘계학술대회B
• /
• pp.2558-2562
• /
• 2007

In the present work, flow characteristics analysis has been performed for steam turbine bypass control valve (single-path type). The numerical analysis is performed by solving three-dimensional Reynolds-averaged Navier-Stokes (RANS) equations. Shear stress transport (SST) model is used as turbulence closure. Symmetry condition is applied at the mid plane of the valve while adiabatic condition is used at the outer wall of the cage. Grid independency test is performed to find the optimal number of grid points. The pressure and temperature distributions on the outer wall of the cage are analyzed. Mass flow rate at maximum plug opening condition is compared with the designed mass flow rate.

• 한국소음진동공학회논문집
• /
• 제23권6호
• /
• pp.502-511
• /
• 2013

Noise performance of small wind turbines is critical since these are generally installed near the community. In this study, flow noise characteristics of Savonius wind turbines are numerically investigated. Flow field around the turbine are computed by solving unsteady RANS equation using CFD techniques and the radiated noise are predicted by applying acoustic analogy to the computed flow data. Parametric study is then carried out to investigate the effects of operating conditions and geometric design factors of the Savonius wind turbine. Tonal noise components with higher harmonic frequency than the BPF are identified in the predicted noise spectra from a Savonius wind turbine. The end-plates and helical blades are shown to reduce overall noise levels. These results can be used to design low-noise Savonius wind turbines.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2009년 추계학술대회논문집
• /
• pp.77-83
• /
• 2009

In this study, we conducted resistance and propulsion performance test of ship composed of the Resistance Test, Propeller Open Water Test and Self Propulsion Test using the CFD(Computational Fluid Dynamics). We used commercial RANS(Reynolds Averaged Navier Stokes equation) solver, as a calculating tool. The unstructured grids were used in a bow and stern of ship, having complex shape, for a convenience of generating grids, and the structured grids were adopted in a central hull and rest of hull having a relatively simple shape which is called hybrid grid method. In addition, The sliding mesh method was adopted to rotate a propeller directly in the Propeller Open Water and Self Propulsion Test. The Resistance Test and Self Propulsion Test were calculated using Volume of Fluid (VOF) model and considering a free surface. And all The three cases were applied realizable k-epsilon model as the turbulence model. The results of calculations were verified for the suitability of calculations by comparing MOERI's EFD results.

• 한국전산유체공학회지
• /
• 제21권1호
• /
• pp.72-77
• /
• 2016

In this study, effects of thurster axis tilting angle on the thruster-hull interaction and propulsion performance in a dynamic positioning system of offshore plant are numerically investigated. Straight and 7-degree tilted downward thruster models as a form of ducted propeller are considered. For numerical simulations, Reynolds averaged Navier-Stokes equations with SST turbulence model are solved by using STAR-CCM+. Results show that thruster-hull interaction is reduced in 7-degree tilted thruster model with lower vortex strength between thruster and hull bottom, although the propulsion performance does not have noticeable difference in a bollard condition.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2010년 춘계학술대회논문집
• /
• pp.341-346
• /
• 2010

In this paper, viscous flow calculation of pump-jet that is used as underwater propulsor was made by using RANS equation. For the validation, calculation for DTRC4119 marine propeller was made and reasonable agreements were obtained between the present results and the experiment. An unstructured overset mesh technique is used for analysis of relative motion between rotor and stator in pump-jet propulsor. Results for pump-jet propulsor were compared with computational results of another researcher.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2006년도 추계 학술대회논문집
• /
• pp.101-105
• /
• 2006

The computational fluid dynamic analysis has been conducted for the thermo-chemical flow field in an arcjet thruster with mono-propellant Hydrazine (N2H4) as a working fluid. The Reynolds Averaged Navier-Stokes (RANS) equations are modified to analyze compressible flows with the thermal radiation and electric field. The Maxwell equation, which is loosely coupled with the fluid dynamic equations through the Ohm heating and Lorentz forces, is adopted to analyze the electric field induced by the electric arc. The chemical reactions of Hydrazine were assumed to be infinitely fast due to the high temperature field inside the arcjet thruster. The chemical and the thermal radiation models for the nitrogen-hydrogen mixture and optically thick media respectively, were incorporated with the fluid dynamic equations. The results show that performance indices of the arcjet thruster with 1kW arc heating are improved by amount of 180% in thrust and 200% in specific impulse more than frozen flow. In addition to thermo-physical process inside the arcjet thruster is understood from the flow field results.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2002년도 학술대회지
• /
• pp.181-184
• /
• 2002

CFD calculations are carried out to investigate the turbulent flow characteristics inside the duct of marine waterjet propulsors. The Reynolds-averaged Wavier-Stokes equations are solved using a finite-volume method. Standard $k-{\varepsilon}$ model and realizable $k-{\varepsilon}$ model are evaluated with an existing experimental data. Multi-block grid topology is adopted to describe the details of complex duct geometry. The present numerical methods are applied to the preliminary duct design of new waterjet propulsor system. Four different influx conditions are simulated to find out pressure and velocity distribution inside the intake duct. Attention is also paid upon the possible flow separation inside the waterjet duct. It is found that CFD tools can be used for the initial evaluation of inflow condition into the impeller of waterjet propulsor system.

• Journal of Advanced Marine Engineering and Technology
• /
• 제39권5호
• /
• pp.548-553
• /
• 2015

The conventional ejector-diffuser system makes use of high pressure primary stream to propel the secondary stream through pure shear action for the purposes of transport or compression of fluid. It has been widely used in many industrial applications such as seawater desalination, solar refrigeration, marine engineering, etc. The present study is performed numerically to study the performance of a two-stage ejector-diffuser system. The detailed flow phenomenon of the ejector-diffuser system has been critically predicted by means of the numerical approach using compressible Reynolds averaged Navier-Stokes (RANS) equations. The axi-symmetric supersonic ejector-diffuser flow has been solved by a fully implicit finite volume scheme with a two-equation k-omega turbulence model. The numerical results are validated with existing experimental data. Detailed flow physics and their contributions on ejector performance are detected to compare both single-stage and two-stage ejectors. The performance improvement on the ejector-diffuser system is discussed in terms of the mass flux ratio and the coefficient of power.